1. Field of Invention
This invention pertains to telecommunications systems, and particularly to the routing of calls through a telecommunications system to an intelligent network service having a non-geographical telephone number.
2. Related Art and Other Considerations
A telecommunications network typically includes a number of physical nodes, often referred to as local exchanges, to which subscribers are connected. The local exchanges are generally connected in the telecommunications network by other physical nodes, known as transit exchanges.
To simply the routing of calls through the network and to have a good structure of a telephone numbering plan, each local exchange is allocated one or more unique exchange number groups. The telephone number of a subscriber typically includes both an exchange number group (typically a 10,000 number block) for the exchange to which a subscriber is connected, and a number in that group which is peculiar to the subscriber. For example, a subscriber having a telephone number"881-1657" is connected to a local exchange having an exchange number group "881", and within that group the subscriber has a subscriber number of "1657". The subscriber's telephone number is published or otherwise circulated as his directory telephone number e.g., in a telephone directory or book.
The foregoing is an example of telephone numbers which are geographical, i.e., for which there is a defined relationship between the telephone number and a geographical area served by the exchange to which the subscriber is connected. For other telephone numbers, referred to as "non-geographical telephone numbers", no geographical relationship exist.
Non-geographical telephone numbers include those associated with services such as services provided by intelligent networks, for example toll-free numbers ("800" in the United States), Freephone, Universal Access Numbers, Personal Numbers, Universal Personal Telecommunications (UPT), Virtual Private Networks (VPNs), International Virtual Private Networks (IVPNs), etc. Such intelligent network (IN)-type services are controlled and executed by a service control point (SCP). For each IN service, data used for the SCP's performance of the IN service typically resides in and is retrieved from a service data function (SDF), which can either be collocated with the SCP or remotely located at a service data point (SDP).
With the advent of pro-competitive regulations for the telephone industry, telecommunications subscribers will be entreated to change telephone service providers. In some instances, a change of telephone service providers has traditionally involved a change of directory telephone number for the subscriber, since differing telephone service providers have differing blocks of numbers in a telephone numbering plan. Changing a directory telephone number undesirably occasions expense and effort for the subscriber. For example, the subscriber incurs expense in providing notice of the new directory number to potential callers (friends and business contacts). If such notice is not provided or retained by the potential callers, calls may not be placed to the relocated subscriber. Loss of calls to a ported subscriber can result in loss of social or business opportunity.
For clarity, what is commonly referred to as a telephone service provider, e.g., a telephone company, will hereinafter be referred to as a telephone service operator (TSO). Unless in context of TSO or otherwise stated, the word "service" hereinafter refers to an intelligent network type of service as is offered by a subscriber e.g., to other subscribers.
If subscribers could retain their original telephone numbers, decisions regarding telephone service operator networks could be based on other factors, such as competitive pricing, quality of service, and service features, for example. Providers of IN services having non-geographical telephone numbers could avail themselves of opportunities for changes of telephone service operators if the providers were assured that their original non-geographical telephone numbers could be retained after the change to a new telephone service operator.
Traditional telephone call routing principles pose a problem for retention of telephone numbers upon a change of telephone service operator. In this regard, a common way of routing a call through a telecommunications network to a final destination is to use the directory telephone number of the called party (e.g., the called subscriber), i.e., the "1-800-xxx-nnnn" for a toll free call. In particular, in traditional routing, the called party's directory telephone number occupies an address signal field of an ISUP parameter known as the "Called Party Number" parameter ("CdPN"), with the "Called Party Number" parameter ("CdPN") being a routing or address message utilized for routing purposes.
What is needed therefore, and an object of the present invention, is an efficient way of permitting a provider of a non-geographic telephone number to retain the non-geographic telephone number when the service provider changes telephone service operators.